Displaying tabs with the monitored shows

Two new methods on the utilDb class: return list of monitored shows;
return list of unseen episodes for a given show.

To the procedure which draws the main frame, I've added the tabs with
the monitored episodes.
Displaying the episodes buttons on the show's tab

The button to set the episode Seen and the play button are now being
displayed on the show's tab
Minor corrections on the scope of the Tabs' work
Minor corrections on the scope of the Tabs' work
Displaying error message when driver is not found

Displaying  an error message on a popup window when we click on the Play
button and the driver specified to get the video file is not found
Merge pull request #4 from anaclcastro/master

Interface enhancement to display the episodes (Issue #2)